ok i got css for christmas, i installed it and steam. when i go to launch it, it loads, the main menu backroud shows up but then my computer restarts. Can anyone help. I would really appretiate it thx.

steam? did you say steam? omg aaaahhhhhhh steam will up your day my friend.

I came across this out of curiosity..... google may help you, or contacting valve too if you get really stuck.
http://forums.bit-tech.net/showthread.php?t=114203

did you get the patches for it?, you need to do that or it will crash.